Java tutorial
/* * Copyright 2002-2018 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.core.io; import java.io.File; import java.io.FileNotFoundException; import java.io.IOException; import java.net.HttpURLConnection; import java.net.URI; import java.net.URL; import java.net.URLConnection; import java.nio.channels.FileChannel; import java.nio.channels.ReadableByteChannel; import java.nio.file.NoSuchFileException; import java.nio.file.StandardOpenOption; import org.springframework.util.ResourceUtils; /** * Abstract base class for resources which resolve URLs into File references, * such as {@link UrlResource} or {@link ClassPathResource}. * * <p>Detects the "file" protocol as well as the JBoss "vfs" protocol in URLs, * resolving file system references accordingly. * * @author Juergen Hoeller * @since 3.0 */ public abstract class AbstractFileResolvingResource extends AbstractResource { @Override public boolean exists() { try { URL url = getURL(); if (ResourceUtils.isFileURL(url)) { // Proceed with file system resolution return getFile().exists(); } else { // Try a URL connection content-length header URLConnection con = url.openConnection(); customizeConnection(con); HttpURLConnection httpCon = (con instanceof HttpURLConnection ? (HttpURLConnection) con : null); if (httpCon != null) { int code = httpCon.getResponseCode(); if (code == HttpURLConnection.HTTP_OK) { return true; } else if (code == HttpURLConnection.HTTP_NOT_FOUND) { return false; } } if (con.getContentLengthLong() > 0) { return true; } if (httpCon != null) { // No HTTP OK status, and no content-length header: give up httpCon.disconnect(); return false; } else { // Fall back to stream existence: can we open the stream? getInputStream().close(); return true; } } } catch (IOException ex) { return false; } } @Override public boolean isReadable() { try { URL url = getURL(); if (ResourceUtils.isFileURL(url)) { // Proceed with file system resolution File file = getFile(); return (file.canRead() && !file.isDirectory()); } else { // Try InputStream resolution for jar resources URLConnection con = url.openConnection(); customizeConnection(con); if (con instanceof HttpURLConnection) { HttpURLConnection httpCon = (HttpURLConnection) con; int code = httpCon.getResponseCode(); if (code != HttpURLConnection.HTTP_OK) { httpCon.disconnect(); return false; } } long contentLength = con.getContentLengthLong(); if (contentLength > 0) { return true; } else if (contentLength == 0) { // Empty file or directory -> not considered readable... return false; } else { // Fall back to stream existence: can we open the stream? getInputStream().close(); return true; } } } catch (IOException ex) { return false; } } @Override public boolean isFile() { try { URL url = getURL(); if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) { return VfsResourceDelegate.getResource(url).isFile(); } return ResourceUtils.URL_PROTOCOL_FILE.equals(url.getProtocol()); } catch (IOException ex) { return false; } } /** * This implementation returns a File reference for the underlying class path * resource, provided that it refers to a file in the file system. * @see org.springframework.util.ResourceUtils#getFile(java.net.URL, String) */ @Override public File getFile() throws IOException { URL url = getURL(); if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) { return VfsResourceDelegate.getResource(url).getFile(); } return ResourceUtils.getFile(url, getDescription()); } /** * This implementation determines the underlying File * (or jar file, in case of a resource in a jar/zip). */ @Override protected File getFileForLastModifiedCheck() throws IOException { URL url = getURL(); if (ResourceUtils.isJarURL(url)) { URL actualUrl = ResourceUtils.extractArchiveURL(url); if (actualUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) { return VfsResourceDelegate.getResource(actualUrl).getFile(); } return ResourceUtils.getFile(actualUrl, "Jar URL"); } else { return getFile(); } } /** * This implementation returns a File reference for the given URI-identified * resource, provided that it refers to a file in the file system. * @since 5.0 * @see #getFile(URI) */ protected boolean isFile(URI uri) { try { if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) { return VfsResourceDelegate.getResource(uri).isFile(); } return ResourceUtils.URL_PROTOCOL_FILE.equals(uri.getScheme()); } catch (IOException ex) { return false; } } /** * This implementation returns a File reference for the given URI-identified * resource, provided that it refers to a file in the file system. * @see org.springframework.util.ResourceUtils#getFile(java.net.URI, String) */ protected File getFile(URI uri) throws IOException { if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) { return VfsResourceDelegate.getResource(uri).getFile(); } return ResourceUtils.getFile(uri, getDescription()); } /** * This implementation returns a FileChannel for the given URI-identified * resource, provided that it refers to a file in the file system. * @since 5.0 * @see #getFile() */ @Override public ReadableByteChannel readableChannel() throws IOException { try { // Try file system channel return FileChannel.open(getFile().toPath(), StandardOpenOption.READ); } catch (FileNotFoundException | NoSuchFileException ex) { // Fall back to InputStream adaptation in superclass return super.readableChannel(); } } @Override public long contentLength() throws IOException { URL url = getURL(); if (ResourceUtils.isFileURL(url)) { // Proceed with file system resolution File file = getFile(); long length = file.length(); if (length == 0L && !file.exists()) { throw new FileNotFoundException(getDescription() + " cannot be resolved in the file system for checking its content length"); } return length; } else { // Try a URL connection content-length header URLConnection con = url.openConnection(); customizeConnection(con); return con.getContentLengthLong(); } } @Override public long lastModified() throws IOException { URL url = getURL(); boolean fileCheck = false; if (ResourceUtils.isFileURL(url) || ResourceUtils.isJarURL(url)) { // Proceed with file system resolution fileCheck = true; try { File fileToCheck = getFileForLastModifiedCheck(); long lastModified = fileToCheck.lastModified(); if (lastModified > 0L || fileToCheck.exists()) { return lastModified; } } catch (FileNotFoundException ex) { // Defensively fall back to URL connection check instead } } // Try a URL connection last-modified header URLConnection con = url.openConnection(); customizeConnection(con); long lastModified = con.getLastModified(); if (fileCheck && lastModified == 0 && con.getContentLengthLong() <= 0) { throw new FileNotFoundException(getDescription() + " cannot be resolved in the file system for checking its last-modified timestamp"); } return lastModified; } /** * Customize the given {@link URLConnection}, obtained in the course of an * {@link #exists()}, {@link #contentLength()} or {@link #lastModified()} call. * <p>Calls {@link ResourceUtils#useCachesIfNecessary(URLConnection)} and * delegates to {@link #customizeConnection(HttpURLConnection)} if possible. * Can be overridden in subclasses. * @param con the URLConnection to customize * @throws IOException if thrown from URLConnection methods */ protected void customizeConnection(URLConnection con) throws IOException { ResourceUtils.useCachesIfNecessary(con); if (con instanceof HttpURLConnection) { customizeConnection((HttpURLConnection) con); } } /** * Customize the given {@link HttpURLConnection}, obtained in the course of an * {@link #exists()}, {@link #contentLength()} or {@link #lastModified()} call. * <p>Sets request method "HEAD" by default. Can be overridden in subclasses. * @param con the HttpURLConnection to customize * @throws IOException if thrown from HttpURLConnection methods */ protected void customizeConnection(HttpURLConnection con) throws IOException { con.setRequestMethod("HEAD"); } /** * Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime. */ private static class VfsResourceDelegate { public static Resource getResource(URL url) throws IOException { return new VfsResource(VfsUtils.getRoot(url)); } public static Resource getResource(URI uri) throws IOException { return new VfsResource(VfsUtils.getRoot(uri)); } } }